Telephone metering system.



E. THOMSON. TELEPHONE METERING SYSTEM. APPLICATION FILED FEB.15, 1912.

1,121,953. Patented M022, 1914.

WITNESSES l JN ENTUH 9 M -ELIHU THUME'DN 1715' AT TDHNEY.

ELIHU THOMSON, OF SWAMLSCOTT, MASSACHUSETTS, ASSIGNDR TO GENERAL ELECTRIC COME'ANY, A CORPORATION OF NEW YORK.

TELEPHONE EQTETERING SYSTEM.

Specification of Letters fatent.

Patented Eec, 22, 19142..

Application filed February 15, 1912. Serial no. 677,82.

To all whom it may concern Beit known that I, Emnn THOMSON, a citizen of the United States, residing at Swampscott, county of Essex, State of Massachusetts, have invented certain new and useful Improvements in Telephone Metering, Systems, of which the following is a specification.

My invention relates to telephone meters,

and particularly to that type of meter which records the length of time a calling subscribers instrument is in use.

The objects of my invention are generally to provide improvements in themethod of operating a telephone circuit so as to actuate a meter located at a subscribers instrument by means of apparatus located at the central exchange.

More specifically, my invention aims at the provision of a method for periodically varying or reversing the direction of flow of the current in a telephone circuit, in which such. changes of current condition actuate the counting train of a meter at the subscribers end of the line.

A further object of invention is' to provide an apparatus for the exchange equipment which will successfully carry out my improved method of operation, an which, in connection with a suitable metering apparatus at thesubscribers end of the line, will satisfactorily register the time the telephone apparatus is in use Without intcrfering with the operation of the same.

Several methods have already been proposed ior indicating by a meter the length of time a telephone is in use, but so far as 1 am aware they have all been open to objection because of the interference which has resulted with the telephone service. This interference has generally consisted inv objectionable noises in the receiving instrument of such an undesirable character asto render the meter apparatus entirely impracticable. My invention eliminates these objectionable features of telephone metering, and provides a method of and means for obtaining an accurate registration of the length of time the telephone is in use with out in any manner interfering with the usual operation of the instrument. Although my invention is adapted to be used in connection with any-type of ,tele' phone meter which depends for its actuaasses ,panying drawing,

of the telephone circuit it is particularly adapted to be used in connection with that type of telephone meter in which the cur rent supplied to the calling subscribers line 18 reversed at short and regular intervals. These reversals of current operate the meter recording mechanism and thus serve to in dicate the length of time the instrument is in'usel. My invention as applied to this type of meter consists in employing a counter electromotive force, as for example, dynamo, induction, to oppose the usual battery log cated at the exchange at periodic intervals of time and simultaneously to impress on the telephone circuit an electromotive force, equal and opposite to that of the battery. It will thus be seen that this counter electromotive force must be twice as large as the electromotive force of the battery, so that the resulting electromotive force causing a ,25

flow of current in the reverse direction to that caused by the battery, is approximately the same as the battery electromotive force. I have found that a generator whose field circuit is periodically opened and closed, furnishes the best source of supply for the counter electromotive force. By properly designing the field of this generator, the length of time required for building up the field and the length of time required for the decay of the same may be'made approximately equal. Under such circumstances, the voltage at the generator terminals will rise very quickly, and at the same time very smoothly, and will thus occasion little or no disturbance in the telephone circuit.

For a better understanding of my invention, reference is to be had to the accomin which the figure shows diagrammatically the novel features of my invention as incorporated in a usual telephone circuit.

In the drawing, where I have shown my invention in connection with that type of meter which depends for its operation upon a reversal of current in the telephone circuit, A and '13 represent the usual telephone instruments of two subscribers. The central exchange outfit is indicated at G. Near each subscribers instrument is placed a me ter which consists broadly of a permanent magnet 55, having the peculiar shaped pole pieces 6 and 'Z' and pivoted armature 9, atla'pted'to he rocked by reversals of the currentin thecoil 8,

telephone circuit, the

tion.

In the circuit of one of the supervisory relays, I include the novel features of mv invention. ture terminals connected across a non-inductive resistance 15 in series with an in ductancc 16 of very low resistance. The resistance 15 is included in the circuit of the supervisory relay. The generator field is excited from any sourceof current, as for example, the direct current mains 1?. A

- clock 18 operates at regular intervals to.

close. the contacts of a relay and this energizes the switch closing mechanism 20. The circuit through the generator field. is thus completed and broken. at regular inter- ;vals and the terminal voltage of the generator is correspondingly varied from full' voltage to Zero.

The voltage of the generator 14 should be, as nearly as possible, twice that of the battery l2. In practice this condition can only be approximated, and it is to be understood that such approximation is entirely satisfactory for the operation of my invention. When the generator 14 is operated, and gen crates approximately twice the voltage of the battery 12, its elcctroinotive force will oppose that of the battery and at the same time reverse the direction of thetlow of current in one side of the circuit, namely, the side in which the generator is located. When the generator field circuit is broken and the battery is supplying current to the direction of flow of the current in the circuit will be as indicated by the full line arrows in the drawings, and when the field circuit is closed by means of the clock and its cooperating mechanism,'and the generator is supplying current to the circuit, the direction of. flow of the current will be shown by the dotted line arrows. When the generator is thus operating under the best conditions no current flows through the battery.

The generator, for the best results, should have a smooth core armature with a commutator having a large number of segments and few armature turns per coil. There should also be two brushes per pole and each brush should span several commutator segments. The smooth core is desirable in The generator is has its arma-' menses order to minimize the humming in the telc-- phone circuit, which would be present f toothed core armature were used. Few turns per coil are employed in order that the change in the inductance of the circuit, due to the armature coils passing beneath the brush, may be as small as possible. 'l brushes should span several commutator segments in order that the current in short circuited armature coil beneath the brush may be brought well within the in flunce of the incoming field before being cut into the circuit. Two brushes per pole are advisable in order to insure a more uniform contact resistance.

The field turns of the generator should be few in order that the time constant may be as small as possible. The decay of the field flux in standard machines is much more rapid than the building up. This is due to the inductance of the field, the electrometive force of which opposes the rapid rise of the current when the field switch is closed.

The time in which a given field will build up depends upon the ratio of the inductance to the resistance, while the rate of decay-do pends upon the design of the machine. Therefore, the most satisfactory result wil be obtained with a given design, when the time of building up is equal to the time decay of the field.

The operation of my device is as follows: When subscriber B takes his receiver vfrom the hook and thus calls the central operator,

the latter will place the answering cord 21,

comprising the usual tip and sleeve, in the proper switchboard jack and will then in.- sert the calling cord 22 in the jack of the second subscriber, l A, who is being called.

The apparatus being thus connected, the

clock periodically, for example, every fifteen seconds, operates the time switch 20, and the generator field is thus regularly and periodically energized. The gradual build ing up and subsequent decay of the generator field produces a corresponding gradual change in the voltage of the generator and thus a reversal of the current is effects without in any way interfering with the telephone circuit. It is desirable to insert the generator in the circuit as quickly and smoothly as possible, in order that the zero of current may be crossed at such a rate as not to interfere with speech. Under such circumstances, there is no interference with the operation of the telephone circuit. The building up and decay of the generator field has been found a most admirable and satisfactory method of inserting a counter electromotive force in the circuit. The rise in l.

up. of the field should be the rapid. The time required for eyident that the meter at the subscribers meter me a that co um i h y, d. as previously stated, the generator is so designed that this result is a omplished.

It will be readily understood by an inspection ef the drawing that only the current in the line of subscriber B is reversed and hence only the meter at Bs instrument records the length of time the telephone is sea The resistance 15 and inductance 16 are not necessary for the satisfactory opera-. tion of my invention. It has been found in practice, however, that the use of these additional elements reduces to zero all humming and objectionable noises in the telephone instruments due to the commutation oi the generator coils.

I do not desire to be limited in the application of my invention to telephone meters which rely specifically on a reversal of current for their operation, since my invention is adapted to be used in connection with any telephone meter which relies for its operation upon a change in the current condition of the telephone circuit. It is end of the line may be operated by varying the current in the telephone circuit instead of by reversing the current, and my invention is adapted to be used in either case.

What I claim as new and desire to secure by Letters Patent of the United States is 1. The method of actuating a meter adapted to he operated by a change in the current condition of a telephone circuit which consists in periodically changing the. supply of the telephone operating current of said circuit, from one source of electromotive force to a separate source of electromotive force, and normally employing the current supplied from each source of electromotive force, for the normal operation of a telephone instrument in said circuit.

2. The method of actuating a meter adapt ed to be operated by a change in the ourrent employed for the normal operation of a telephone instrument in said circuit which consists in periodically changing the supply of current to said circuit for the operation of said instrument from one source of electromotiye force to aseparate source of elec-' tromotive force, so that the flow of the telephone operating current is altered by each periodic change of the source of supply of electromotive force The method of actuating a meter adapted to be operated by varying the current in a telephone circuit which consists in maintaining a source of potential connected to i said circuit and periodically opposing said seurce of potential by a second source of po-' si ti la The method of actuating a meter adapted to be operated by varying the current in a telephone circuit which consists in maintaining a' source of potential connected to said circuit, periodically opposing said source of potential by a second source of potential and simultaneously supplying .current to said circuit from said second source of potential.

The method of actuatipg a meter adapted to be operated by arying the current in a telephone circuit, which consists in maintaining a battery and an electric generator connected to said circuit, periodically energizing the field of said generator and employing the resulting electromotive force to oppose the electromotive force of said batter'y and to supply current to said circuit.

6. -The method of actuating-ameter adapted to be operated by reversing the current in a telephone circuit that employs abattery as a source of current, which consists in opposing the battery by dynamo induction and simultaneously supplying a reversed current to the circuit.

7. The method of actuating a meter adapted to be operated by reversing the direction of fiow of current in a telephone circuit, which consists in opposing the electromotive force of the primary source of current by current to said circuit from said generator in a direction reversed to that due to the primary source.

' 8. The method of actuating a meter adapted to be operated by periodically reversing the direction of flow of current in a telephone circuit, which consists in main taining a source of potential connected to said circuit, periodically opposing said source of potential by a second source of potential and simultaneously impressing on said circuit a potential equal and opposite to said first source.

9. The method of actuating a meter adapted to be operated byperiodically reversing the direction of flow of current in a telephone circuit, which consists in maintaining a storage battery and a generator connected to said circuit, periodically energizing the field of said generator and utilizing the resulting electromotive force to oppose the electromotive force of the battery and to supply the circuit With current in the reversed direction to that supplied by the battery.

1.0. The method of actuating a, meter adapted to be operated by periodically reversing the direction of flow of currentin a telephone circuit, which consists in maintaining a source of potential connected to said circuit, periodically generating a second source of potential and employing said second source of potential to oppose said first source and also to supply current to said circuit in a reverse'd'direction to that supplied by said first source.

use

,11. The method of actuating a meter adapted to be. operated by periodically rcvcrsing the direction of flow of current in a telephone circuit, which consists in main taining a storage battery-and av generator Whose full voltage is approximately twice that of the battery connected to said circuit, periodically energizing the field or said generator and employing the resulting; electromotire force of the generator to oppose the electromotire force of the battery and simultaneously supplying; current to the circuit from the generator in a reversed direc tion to that supplied by the battery.

12. In a telephone circuit, a meter adapt cd to be operated by a change in the current condition of the telephone circuit, a source of current connected to said circuit, and means for periodically opposing during the period that a telephone instrument in said circuit is in use the electromotive force of said source of current.

'13. In a telephone circuit, a meter adapted to be operated bya change in the current condition of the telephone circuit, a source otsurrent connected to said circuit, and means for periodically opposing the elec tromotive force of said source of current and for simultaneously supplying current to said circuit.

14. In a telephone circuit, a meter adapted to be operated by' a change in the current condition of the telephone circuit, a. source of current connected to said circuit, and means for periodically opposing the electrornotire force of said source of current and for simultaneously supplying current to said circuit in a reversed direction to that supplied by said source.

15. In a telephone circuit, a meter adapted to be operated by a change in the current condition of the telephone circuit, a battery connected to said circuit, and means for periodically opposing during the period that a telephone instrument in said circuit is in use the electromotive force of said battery by dynamo induction.

16. In a telephone circuit, a meter-adapted to be operated by a change in the current condition of the telephone circuit, a battery and a generator connected to said circuit, and means for periodically opposing during the period that atelephone instrument in said circuit is in use the electromotive force of the battery by the electromotive force of the generator.

17. In a telephone circuit, a meter adapted to be operated by a change in the current condition of the telephone circuit, a battery connected to said circuit, and means for periodically opposing the electroinotire force of the battery and for simultaneously sup plying current to said circuit.

18. In a telephone circuit, a meter ed to be operated by a change in the ct condition of the telephone circuit, independent sources of electroniotivc for supplying current to said means for periodically opposii tromotire force of one said the electromotive force of the other sources and for supplying current to circuit from said last mentioned source.

19. In a telephone circuit, a r. er a to be operated by a change in the c. condition of the telephone circuit, a $01.. of current connected to said circuit, on elec-- tric generator connected to circuit, a means for periodically opposing din period that a telephone instrument in a circuit is in use the electrornotive force o said source by the electroinotive force said generator.

20. .ln a telephone circuit, a meter adapted to be operated by a change in the current condition of the telephone circuit, a source of current connected to said circuit, an electric generator, means for periodically ener during the period that a telephone i in said circuit is in use the field c 1 orator, and electrical connections I01 opposing the electrornotivc force of said source by the resulting electrornotivc. force said generator.

21. In a. telephone-circuit, a meter to be operated by a change in the current condition. of the telephone circuit, a source of current connected to said circuit, an elcctrio generator, means for periodically ener gizing the field. of said generator, and electrical connections for opposing the electro motive force of said source by the resul'ing electromotive force of the generator and simultaneously supplying current to s... circuit from said generator.

In a telephone circuit, a meter adap to be operated by a change in the cur condition of the telephone circuit, a battery generator to oppose the electromotiye force of said battery and for simultaneously supplying current to sa d circult by said gen orator.

2-2;. In a telephone circuit, a meter adapted to be operated by a change in the current condition of the telephone circuit, a battery connected to said circuit, an electric gener ator having its armature terminals con nected to a nondnductive resistance in series with inductance, connections'between the non-inductive resistance and the circuit so that the voltage across said resistance opposes the electromotive force of the battery. when the generator field is energized, and means for periodically energizing the field of said generator. r

25. In a telephone circuit, a meter adapted to be operated by a change in the current condition of the telephone circuit, a battery connected to said circuit, an electric genorator whose normal electromotiveiorce is approximately twice that of the battery, and means for periodically opposing the electroniotive force of the battery by the electromotive force of the generator and simultaneously supplying current to the circuit from said generator.

26. In a telephone circuit, a meter adapted to be operated by a change in the current means for periodically impressing on said' resistance during the period that a telephone instrument in said circuit 1s m use an electromotive force approximately twice,

as great as the electromotive force of the battery and opposite in direction.

In Witness Whe'reoflI have hereunto set' my hand this 13th day of February 1912 ELIHU THOMSON.

Witnesses "Jorm A. MCMANUS, Jr., FRANK G. Han a, J 

